Naval Ocean Systems Center Research Articles

Acoustic variability due to intrusive Arctic finestructure

A previous paper [J. Acoust. Soc. Am. 64, S22 (1978)] discussed the results of acoustic transmission measurements in the frequency range of 10 to 60 kHz, in the presence of layered, thermal finestructure under an arctic ice island. “Layered finestructure” refers to relatively stable, slowly, changing thermal layers in the ocean that have a vertical scale of about a meter to tens of meters. Their horizontal extent may be 10 to 100 times larger. Acoustic transmission was found to be strongly affected by the presence, near the transmitter, of a layer or layers with a sound speed maximum or minimum. In the present paper, additional spectral and statistical properties of the acoustical field are presented, including dependence on ray angle, range, and frequency. Some attempt is made to relate these acoustic properties to oceanographic properties of the medium. [Work supported by Arctic Submarine Laboratory of the Naval Ocean Systems Center, San Diego, CA.]

Possible evolutionary affinities seen in sea snake venom-antivenom reactions: George V. Pickwell Marine Sciences Division, Naval Ocean Systems Center, San Diego, California, U.S.A.

Possible evolutionary affinities seen in sea snake venom-antivenom reactions: George V. Pickwell Marine Sciences Division, Naval Ocean Systems Center, San Diego, California, U.S.A.

Experiences with sea snake antivenins and antitoxins: George V. Pickwell Marine Sciences Division, Naval Ocean Systems Center, San Diego, California, USA

Experiences with sea snake antivenins and antitoxins: George V. Pickwell Marine Sciences Division, Naval Ocean Systems Center, San Diego, California, USA

Low-frequency normal modes using improved phase integral methods

Normal mode (NM) theory provides a solution to sound propagation in an inhomogeneous ocean. Use of NM theory is, however, restricted by the ease with which depth eigenfunctions Φn and eigenvalues λn satisfying d2Φn/dz2 + [w2/c2(z) − λn] Φn = 0, plus boundary conditions, may be computed. Employing generalized Langer transformations, uniform asymptotic expansions to Φn, are obtained in terms of parabolic cylinder functions for realistic sound velocity profiles (SVP). The expansions are valid at turning points, require no connection formulae (unlike WKB), and yield complex eigenvalues. The method is asymptotic to A = (2πfh/c0)2 with f denoting frequency, h the SVP scale depth, and c0 the axial sound speed. For deep ocean A ∼ (2f)2, indicating useability to frequencies as low as 3–5 Hz. Results of calculations for Munk's canonical SVP: c(η) = c0 (1 + ε[e−η + η − 1]), η = (z − z0)/h will be described. Extensions to range-dependent environments and inclusion of arbitrary surface and bottom boundary conditions will be discussed. [Supported in part by Naval Ocean Systems Center.]

New fidelity criteria and encoding strategies for acoustic data compression

A study of fidelity criteria (i.e., distortion measures) appropriate for data compression of passive sonar signals was conducted. The classical mean squared error (MSE) criterion was found to be a poor choice for this application, as well as other applications wherein the source signal is to be spectrum analyzed. Two new fidelity criteria, the mean incoherence (MIC) and mean log-coherence (MLC), were developed and tested on passive sonar type signals. The experimental results indicated that these criteria provide an accurate assessment of the distortion produced by a data compression system on this type of signal. The rate-distortion functions of a Gaussian source signal, subject either to MIC or MLC fidelity requirements, were then derived. These functions specify the minimum transmission rate (e.g., bits/sample) required in order to reproduce the source signal with a given distortion. Also, the analysis indicates the effect of optimum encoding on the source signal power spectrum. A number of near-optimum encoding schemes were then developed for these new fidelity criteria. [Work supported by Naval Ocean Systems Center.]

Underwater repetitive mammal sound sequences in the Bering Strait

Much attention has been directed in the last eight years to the “songs” of the humpback whale, Megaptera novaeangliae, the only known cetacean to produce a complex sequence of sounds that is repeated substantially unchanged for hours at a time. Mammal sounds in similar (but simpler) “song” sequences were tape recorded by the Naval Ocean Systems Center in the ice‐covered Bering Strait on two occasions separated by several months. Although the sounds and sequences in the two recordings were clearly different, they are believed to be from the same species. Among possible sources of the sounds are the walrus, Odobenus rosmarus, and the bowhead whale, Balaena mysticetus. Analyses of the sound patterns and arguments on sound source identification will be presented.

Acoustic variability due to layered finestructure in the Arctic

Acoustic transmission measurements, in the frequency range 10–60 kHz, have been carried out in the presence of layered, thermal fine structure under arctic ice. The term “layered fine structure” refers to relatively stable, slowly changing thermal layers in the ocean that have a vertical scale of about a meter to several meters. Their horizontal extent may be 10–100 times larger. In these measurements, acoustic transmission is strongly affected by the presence, near the transmitter, of a layer or layers with a sound speed maximum. In the literature these warm layers are sometimes called “antiwaveguide” or “barrier” layers. Three types of space-time variability have been found in the received intensity versus depth records: (1) A small random variability observed at relatively steep transmission angles, (2) a frequency-independent variability which can be related to convergence/divergence of rays in the refraction field of the layer, and (3) a frequency-dependent variability which seems to arise from the interference between direct rays and those sharply refracted by the layer. A spectral analysis of the interference region confirms that the spatial wavelength in depth is inversely proportional to the acoustic frequency. [Work supported by Arctic Submarine Laboratory of the Naval Ocean Systems Center, San Diego, CA.]

<title>Forum: Radiometry And Photometry</title>

My column this month is a review of the seminar on Utilization of Infrared Detectors that was presented on January 17 and 18, 1978, at the Sheraton Universal Hotel in North Hollywood, California. This seminar, organized by Wesley L. (Lum) Eisenman of the Naval Ocean Systems Center, was devoted to materials, testing, astronomy, and devices.

Directional VLF sferics from the Union City, Oklahoma, tornadic storm

The Naval Electronics Laboratory Center (now Naval Ocean Systems Center) made directional measurements of very low frequency sferics in the Union City, Oklahoma, tornadic storm on May 24, 1973. These data verify the interesting findings of two earlier directional sferics studies. Whereas sferics activity in tornado‐producing storms is known to peak near tornado time, all these studies show conclusively that sferics do not originate in the tornado itself but rather throughout the parent thunderstorm.

Coordinated measurements of ELF transmission anomalies and the precipitation of energetic particles into the ionosphere

Stimulated by previous findings of a positive qualitative correlation between anomalous ELF signal levels and the occurrence of significant fluxes of precipitating energetic particles, coordinated exercises were conducted between satellite measurements of the precipitating particles and ELF transmissions between the US Navy Wisconsin Test Facility and receiving stations in Maryland, Greenland, Norway, and Italy. Significant fluxes of precipitating electrons were often measured with the Lockheed pay load on the polar‐orbiting satellite 1972–076B. In March‐April 1976 the received signal strengths were found generally to increase during periods when the geomagnetic K indices were higher and when the fluxes of precipitating electrons >160 keV were greater on the average. During other coordinated exercises in March‐April 1975 the general correlations were less evident. Based on the fluxes, energy spectra, and pitch‐angle distributions of the particles, ion‐pair production profiles have been calculated and electron density profiles subsequently obtained with application of known effective electron loss rates. From the coordinated data, correlative studies between signal strengths and electron density profiles have been performed with use of an ELF waveguide mode computer program developed at the Naval Ocean Systems Center. The propagation path to each station of interest is segmented into different regions with an averaging perpendicular to the direction of propagation of the waveguide parameters. With the inclusion of data from several stations, the transmission signal strengths could be studied simultaneously under a variety of ionospheric conditions. The waveguide computer program calculations indicated that energetic electron precipitation events may cause a signal enhancement or degradation, depending upon where the disturbance is occurring along the path. The consistent occurrence during electron precipitation events of signal strength anomalies in either direction is supported by the coordinated satellite/ELF station measurements.

Effects of temperature on the aging rate of piezoelectric polymer

Results of aging measurements at 20°C, 57°C, and 66°C are presented for commercially available piezoelectric polymer (28-μm thick, poled polyvinylidene fluoride). The g31 (electric field/stress) and d31 (charge density/stress) piezoelectric constants were measured by a static dead weight tension test. The relative dielectric constant K33T was obtained from a 1-kHz capacitance measurement. At room temperature (20°C), aging rates of 10%/time decade for g31, 15%/time decade for d31, and 7%/time decade for K33T were obtained over a 100-day period from date of poling. Values of g31 and K33T were measured (at room temperature) for samples held at 57°C and 66°C for 100 days starting at 400 days from poling. For the 57°C case, g31 values at 401, 410, and 500 days showed a 3%, 10%, and 16% decrease over the 400-day value. The 66°C case showed decreases of 16%, 19%, and 21% in g31 over the same time period. No change in K33T was observed for either of these cases. [Work supported by R. R. Smith, Code 302, Naval Ocean Systems Center, San Diego, CA.]

Microcomputer-based system for speech synthesis from a large English text data base

The basic goal for the described project is selective and interactive production of synthetic speech from a large data base such as a training manual. In a training environment at a sophisticated computer control console, an operator should learn more effectively and efficiently if both aural and visual senses are used and if his eyes and hands are free to concentrate on the panel before him. The system described includes an operator-directed control strategy to selectively retrieve that part of text which is to be spoken, a considerable amount of text preprocessing in non-real time to obtain synthesizer control parameters, and a microcomputerized cascade terminal analog speech synthesizer. The preprocessing of the English text utilizes an extensive set of translation rules, dictionary lookup of complete words, and morph lexicon lookup of parts of words to produce 123 distinct allophone designators with corresponding stress, pitch, and duration designators. Storage requirements for the preprocessed speech control parameters to be supplied to the real-time speech synthesized are approximately 120 bits/sec of synthesized speech. Example recordings of the synthetic speech produced by this system will be presented. [Work supported by the Naval Ocean Systems Center.]